Separation of traces of copper(II) from iron(III) with 8-quinolinol-impregnated emulsion globules

A chelating agent-impregnated w/o emulsion was prepared by dissolving 50 mg of 8-quinolinol and 0.15 ml of Span-80 (nonionic surfactant) in 5 ml of toluene and then mixing with 1.5 ml of 1 mol/l hydrochloric acid by ultrasonic irradiation (20 kHz) for 15 s. The resulting emulsion was added to 25 ml of a sample and dispersed by stirring for 5 min as numerous small globules (0.1 similar to 0.5 min in diam.). Copper(II) ions in the sample were quantitatively diffused through the toluene layer into small droplets of hydrochloric acid at pH3 similar to 7. The emulsion was separated and heated at 80 similar to 90 degreesC to segregate the aqueous (hydrochloric acid) and organic (toluene) phases. The copper in the aqueous phase was determined by graphite-furnace atomic absorption spectrometry. The recovery of copper(II) in the presence of iron (111) was successfully achieved with a yield of greater than 95% at pH3 similar to 3.5, where the iron (III) existed as colloidal hydroxide particles and did not penetrate into the emulsion. This discrimination may be attributed to the surfactant layer at the oil-water interfaces. At higher pH's, however, the iron(III) colloids coagulated to form bulky hydroxide precipitates, on which most of the copper(II) ions were coprecipitated. The proposed emulsion method has been applied to the determination of copper at low mug/g levels in high-purity iron metals.